The conversion of hexavalent molybdenum (Mo (VI)) to Mo-blue is a bioremediation technique
which reduces the toxicity of molybdenum to a less toxic form by bacteria. The aim of this study
is to determine the optimum conditions of significant parameters or variables that affect the
reduction of Mo (VI) to Mo-blue by the local isolate identified as Serratia sp. strain MIE2.
Response Surface Methodology (RSM) was used in this study to optimize the reduction process
using Central Composite Design (CCD) as an optimization matrix. The optimum conditions
predicted by RSM using the desirability function for the reduction process were 20 mM
molybdate concentration, 3.95 mM phosphate, 6.25 pH and 25 g/L glucose and Mo-blue
production occurred at the absorbance value of 20.5 at 865 nm. The validation of the predicted
optimum points showed the Mo-blue production occurred at the absorbance value of 21.85 with
a deviation around 6.6 % from the RSM predicted value.
Petroleum pollution is a major concern in Antarctica due to the persistent nature of its hydrocarbon components coupled with the region's extreme environmental conditions, which means that bioremediation approaches are largely inapplicable at present. The current study assessed the ability of the psychrotolerant phenol-degrader, Rhodococcus sp. strain AQ5-07, to assimilate diesel fuel as the sole carbon source. Factors expected to influence the efficiency of diesel degradation, including the initial hydrocarbon concentration, nitrogen source concentration and type, temperature, pH and salinity were studied. Strain AQ5-07 displayed optimal cell growth and biodegradation activity at 1% v/v initial diesel concentration, 1 g/L NH4Cl concentration, pH 7 and 1% NaCl during one-factor-at-a-time (OFAT) analyses. Strain AQ5-07 was psychrotolerant based on its optimum growth temperature being near 20 °C. In conventionally optimised media, strain AQ5-07 showed total petroleum hydrocarbons (TPH) mineralisation of 75.83%. However, the optimised condition for TPH mineralisation predicted through statistical response surface methodology (RSM) enhanced the reduction to 90.39% within a 2 days incubation. Our preliminary data support strain AQ5-07 being a potential candidate for real-field soil bioremediation by specifically adopting sludge-phase bioreactor system in chronically cold environments such as Antarctica. The study also confirmed the utility of RSM in medium optimisation.
Study of the potential of Antarctic microorganisms for use in bioremediation is of increasing interest due to their adaptations to harsh environmental conditions and their metabolic potential in removing a wide variety of organic pollutants at low temperature. In this study, the psychrotolerant bacterium Rhodococcus sp. strain AQ5-07, originally isolated from soil from King George Island (South Shetland Islands, maritime Antarctic), was found to be capable of utilizing phenol as sole carbon and energy source. The bacterium achieved 92.91% degradation of 0.5 g/L phenol under conditions predicted by response surface methodology (RSM) within 84 h at 14.8 °C, pH 7.05, and 0.41 g/L ammonium sulphate. The assembled draft genome sequence (6.75 Mbp) of strain AQ5-07 was obtained through whole genome sequencing (WGS) using the Illumina Hiseq platform. The genome analysis identified a complete gene cluster containing catA, catB, catC, catR, pheR, pheA2, and pheA1. The genome harbours the complete enzyme systems required for phenol and catechol degradation while suggesting phenol degradation occurs via the β-ketoadipate pathway. Enzymatic assay using cell-free crude extract revealed catechol 1,2-dioxygenase activity while no catechol 2,3-dioxygenase activity was detected, supporting this suggestion. The genomic sequence data provide information on gene candidates responsible for phenol and catechol degradation by indigenous Antarctic bacteria and contribute to knowledge of microbial aromatic metabolism and genetic biodiversity in Antarctica.
At present, polyhydroxyalkanoates (PHAs) have been considered as a promising alternative to conventional plastics due to their diverse variability in structure and rapid biodegradation. To ensure cost competitiveness in the market, thermoseparating aqueous two-phase extraction (ATPE) with the advantages of being mild and environmental-friendly was suggested as the primary isolation and purification tool for PHAs. Utilizing two-level full factorial design, this work studied the influence and interaction between four independent variables on the partitioning behavior of PHAs. Based on the experimental results, feed forward neural network (FFNN) was used to develop an empirical model of PHAs based on the ATPE thermoseparating input-output parameter. In this case, bootstrap resampling technique was used to generate more data. At the conditions of 15 wt % phosphate salt, 18 wt % ethylene oxide⁻propylene oxide (EOPO), and pH 10 without the addition of NaCl, the purification and recovery of PHAs achieved a highest yield of 93.9%. Overall, the statistical analysis demonstrated that the phosphate concentration and thermoseparating polymer concentration were the most significant parameters due to their individual influence and synergistic interaction between them on all the response variables. The final results of the FFNN model showed the ability of the model to seamlessly generalize the relationship between the input⁻output of the process.
The performance of a compost biofilter inoculated with mixed microbial consortium was optimized for treating a gas-phase mixture of benzene and toluene. The biofilter was acclimated to these VOCs for a period of ∼18d. The effects of concentration and flow rate on the removal efficiency (RE) and elimination capacity (EC) were investigated by varying the inlet concentration of benzene (0.12-0.95g/m(3)), toluene (0.14-1.48g/m(3)) and gas-flow rate (0.024-0.072m(3)/h). At comparable loading rates, benzene removal in the mixture was reduced in the range of 6.6-41% in comparison with the individual benzene degradation. Toluene removal in mixture was even more affected as observed from the reductions in REs, ranging from 18.4% to 76%. The results were statistically interpreted by performing an analysis of variance (ANOVA) to elucidate the main and interaction effects.
Major degraders of petroleum hydrocarbons in tropical seas have been indicated only by laboratory culturing and never through observing the bacterial community structure in actual environments. To demonstrate the major degraders of petroleum hydrocarbons spilt in actual tropical seas, indigenous bacterial community in seawater at Sentosa (close to a port) and East Coast Park (far from a port) in Singapore was analyzed. Bacterial species was more diverse at Sentosa than at the Park, and the composition was different: γ-Proteobacteria (57.3%) dominated at Sentosa, while they did not at the Park. Specialized hydrocarbonoclastic bacteria (SHCB), which use limited carbon sources with a preference for petroleum hydrocarbons, were found as abundant species at Sentosa, indicating petroleum contamination. On the other hand, SHCB were not the abundant species at the Park. The abundant species of SHCB at Sentosa were Oleibacter marinus and Alcanivorax species (strain 2A75 type), which have previously been indicated by laboratory culturing as important petroleum-aliphatic-hydrocarbon degraders in tropical seas. Together with the fact that SHCB have been identified as major degraders of petroleum hydrocarbons in marine environments, these results demonstrate that the O. marinus and Alcanivorax species (strain 2A75 type) would be major degraders of petroleum aliphatic hydrocarbons spilt in actual tropical seas.
Steroid estrogens, such as estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethinylestradiol (EE2), are natural and synthetic hormones released into the environment through incomplete sewage discharge. This review focuses on the sources of steroid estrogens in wastewater treatment plants (WWTPs). The mechanisms and fate of steroid estrogens throughout the entire wastewater treatment system are also discussed, and relevant information on regulatory aspects is given. Municipal, pharmaceutical industry, and hospitals are the main sources of steroid estrogens that enter WWTPs. A typical WWTP comprises primary, secondary, and tertiary treatment units. Sorption and biodegradation are the main mechanisms for removal of steroid estrogens from WWTPs. The fate of steroid estrogens in WWTPs depends on the types of wastewater treatment systems. Steroid estrogens in the primary treatment unit are removed by sorption onto primary sludge, followed by sorption onto micro-flocs and biodegradation by microbes in the secondary treatment unit. Tertiary treatment employs nitrification, chlorination, or UV disinfection to improve the quality of the secondary effluent. Activated sludge treatment systems for steroid estrogens exhibit a removal efficiency of up to 100%, which is higher than that of the trickling filter treatment system (up to 75%). Moreover, the removal efficiency of advance treatment systems exceeds 90%. Regulatory aspects related to steroid estrogens are established, especially in the European Union. Japan is the only Asian country that implements a screening program and is actively involved in endocrine disruptor testing and assessment. This review improves our understanding of steroid estrogens in WWTPs, proposes main areas to be improved, and provides current knowledge on steroid estrogens in WWTPs for sustainable development.
The sorption characteristics of Cr(VI) and Cu(II) by ethylenediamine modified rice hull from single and binary metal ion solutions were evaluated under various experimental conditions. Optimal Cr(VI) and Cu(II) removal from single metal ion solutions occurred at pH 2.0 and 5.5, respectively. Simultaneous removal of Cr(VI) and Cu(II) occurred at pH greater than 3.0. The sorption kinetics of Cr(VI) and Cu(II) from single and binary metal ion solutions were studied with reference to metal concentration, agitation rate and particle size. Sorption of Cr(VI) was more rapid than Cu(II). The kinetics of metal ion sorption fitted a pseudo-second order expression. The variation in the initial uptake rates was very small at an agitation rate beyond 150 rpm and sorption was generally independent of particle size. Equilibrium sorption data could be fitted into the Langmuir isotherm equation. Maximum sorption capacities of ethylenediamine modified rice hull for Cr(VI) at pH 2 and Cu(II) at pH 4 in single metal solutions were 0.45 and 0.06 mmol g(-1), respectively. This corresponds to an enhancement factor of 2.6 and 3 fold for Cr(VI) and Cu(II), respectively, compared to natural rice hull. A synergistic effect was observed for sorption of these ions in binary metal solutions.
An air exposed single-chamber microbial fuel cell (SCMFC) using microalgal biocathodes was designed. The reactors were tested for the simultaneous biodegradation of real dye textile wastewater (RTW) and the generation of bioelectricity. The results of digital image processing revealed a maximum coverage area on the biocathodes by microalgal cells of 42%. The atmospheric and diffused CO2 could enable good algal growth and its immobilized operation on the cathode electrode. The biocathode-SCMFCs outperformed an open circuit voltage (OCV), which was 18%-43% higher than the control. Furthermore, the maximum volumetric power density achieved was 123.2 ± 27.5 mW m(-3). The system was suitable for the treatment of RTW and the removal/decrease of COD, colour and heavy metals. High removal efficiencies were observed in the SCMFCs for Zn (98%) and COD (92-98%), but the removal efficiencies were considerably lower for Cr (54-80%). We observed that this single chamber MFC simplifies a double chamber system. The bioelectrochemical performance was relatively low, but the treatment capacity of the system seems encouraging in contrast to previous studies. A proof-of-concept experiment demonstrated that the microalgal biocathode could operate in air exposed conditions, seems to be a promising alternative to a Pt cathode and is an efficient and cost-effective approach to improve the performance of single chamber MFCs.
Biological removal of carbon, nitrogen and sulfur is drawing increasing research interest in search for an efficient and cost-effective wastewater treatment. While extensive work on separate removal of nitrogen and sulfur is well documented, investigation on simultaneous denitrifying sulfide removal has only been reported recently. Most of the work on denitrifying sulfide removal has been focusing on bioreactor performance, loading and operating conditions. Nonetheless, underlying principles elucidating the biochemical reactions and the mechanisms of the microbial degradation are yet to be established. In addition, unstable denitrifying sulfide removal which is a major operating problem that hinders practical application of the process, is yet to be resolved. This paper provides a review on the state-of-the-art development of simultaneous biological removal of sulfur, nitrogen and carbon. Research on bioreactor operation and performance, reactor configurations, mechanisms and modeling work including the use of mass balance analysis and artificial neural networks is delineated. An in-depth discussion on the microbial community and functional consortium is also provided. Challenges and future work on simultaneous biological removal of nitrogen-sulfur-carbon are also outlined.
The application of simultaneous adsorption and biodegradation processes in the same reactor is known to be effective in the removal of both biodegradable and non-biodegradable contaminants in various kinds of wastewater. The objective of this study is to evaluate the efficacy of the two processes under sequencing batch reactor (SBR) operation in treating copper and cadmium-containing synthetic wastewater with powdered activated carbon (PAC) as the adsorbent. The SBR systems were operated with FILL, REACT, SETTLE, DRAW and IDLE periods in the ratio of 0.5: 3.5: 1.0: 0.75 :0.25 for a cycle time of 6 h. In the presence of 10 mg/L Cu(II) and 30 mg/L Cd(II), respectively, the average COD removal efficiencies were above 85% with the PAC dosage in the influent solution at 143 mg/L compared to around 60% without PAC addition. Copper(II) was found to exert a more pronounced inhibitory effect on the bioactivity of the microorganisms compared to Cd(II). It was observed that the combined presence of Cu(II) and Cd(II) did not exert synergistic effects on the microorganisms. Kinetic study conducted for the REACT period showed that the addition of PAC had minimized the inhibitory effect of the heavy metals on the bioactivity of microorganisms.
Microbial fuel cells (MFCs) represent one of the most attractive and eco-friendly technologies that convert chemical bond energy derived from organic matter into electrical power by microbial catabolic activity. This paper presents the use of a H-type MFC involving a novel NAR-2 bacterial consortium consisting of Citrobacter sp. A1, Enterobacter sp. L17 and Enterococcus sp. C1 to produce electricity whilst simultaneously decolourising acid red 27 (AR27) as a model dye, which is also known as amaranth. In this setup, the dye AR27 is mixed with modified P5 medium (2.5 g/L glucose and 5.0 g/L nutrient broth) in the anode compartment, whilst phosphate buffer solution (PBS) pH 7 serves as a catholyte in the cathode compartment. After several electrochemical analyses, the open circuit voltage (OCV) for 0.3 g/L AR27 with 24-h retention time at 30 °C was recorded as 0.950 V, whereas (93%) decolourisation was achieved in 220-min operation. The maximum power density was reached after 48 h of operation with an external load of 300 Ω. Scanning electron microscopy (SEM) analysis revealed the surface morphology of the anode and the bacterial adhesion onto the electrode surface. The results of this study indicate that the decolourisation of AR27 dye and electrical power generation was successfully achieved in a MFC operated by a bacterial consortium. The consortium of bacteria was able to utilise AR27 in a short retention time as an electron acceptor and to shuttle the electrons to the anode surface for bioelectricity generation.
In this study, a twin-chamber upflow bio-electrochemical reactor packed with palm shell granular activated carbon as biocarrier and third electrode was used for sequential nitrification and denitrification of nitrogen-rich wastewater under different operating conditions. The experiments were performed at a constant pH value for the denitrification compartment. The effect of variables, namely, electric current (I) and hydraulic retention time (HRT), on the pH was considered in the nitrification chamber. The response surface methodology was used based on three levels to develop empirical models for the study on the effects of HRT and current values as independent operating variables on NH(4)(+)-N removal. The results showed that ammonium was reduced within the function of an extensive operational range of electric intensity (20-50 mA) and HRT (6-24h). The optimum condition for ammonium oxidation (90%) was determined with an I of 32 mA and HRT of 19.2h.
Petroleum hydrocarbons remain as the major contaminants that could be found across the world.
Remediation approach through the utilisation of microbes as the bioremediation means widely
recognised due to their outstanding values. As a result, scientific reports on the isolation and
identification of new hydrocarbon-degrading strains were on the rise. Colourimetric-based assays
are one of the fastest methods to identify the capability of hydrocarbon-degrading strains in both
qualitative and quantitative assessment. In this study, the hydrocarbon-degrading potential of
nine bacterial isolates was observed via 2,6-dichlorophenolindophenol (DCPIP) test. Two potent
diesel-utilising isolates show a distinctive tendency to utilise aromatic (ADL15) and aliphatic
(ADL36) hydrocarbons. Both isolates prove to be a good candidate for bioremediation of wide
range of petroleum hydrocarbon components.
The continuous accumulation of microplastics in the environment poses ecological threats and has been an increasing problem worldwide. In this study, eight bacterial strains were isolated from mangrove sediment in Peninsular Malaysia to mitigate the environmental impact of microplastics and develop a clean-up option. The bacterial isolates were screened for their potential to degrade UV-treated microplastics from polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), and polystyrene (PS). Only two isolates, namely, Bacillus cereus and Bacillus gottheilii, grew on a synthetic medium containing different microplastic polymers as the sole carbon source. A shake flask experiment was carried out to further evaluate the biodegradability potential of the isolates. Degradation was monitored by recording the weight loss of microplastics and the growth pattern of the isolates in the mineral medium. The biodegradation extent was validated by assessment of the morphological and structural changes through scanning electron microscopy and Fourier transform infrared spectroscopy analyses. The calculated weight loss percentages of the microplastic particles by B. cereus after 40 days were 1.6%, 6.6%, and 7.4% for PE, PET, and PS, respectively. B. gottheilii recorded weight loss percentages of 6.2%, 3.0%, 3.6%, and 5.8% for PE, PET, PP, and PS, respectively. The designated isolates degraded the microplastic material and exhibited potential for remediation of microplastic-contaminated environment. Biodegradation tests must be conducted to characterize the varied responses of microbes toward pollutants, such as microplastics. Hence, a novel approach for biodegradation of microplastics must be developed to help mitigate the environmental impact of plastics and microplastic polymers.
This study aimed to isolate biosurfactant-producing and hydrocarbon-degrading actinomycetes from different soils using glycerol-asparagine and starch-casein media with an antifungal agent. The glycerol-asparagine agar exhibited the highest number of actinomycetes, with a white, low-opacity medium supporting pigment production and high growth. Biosurfactant analyses, such as drop collapse, oil displacement, emulsification, tributyrin agar test, and surface tension measurement, were conducted. Out of 25 positive isolates, seven could utilize both olive oil and black oil for biosurfactant production, and only isolate RP1 could produce biosurfactant when grown in constrained conditions with black oil as the sole carbon source and inducer, demonstrating in situ bioremediation potential. Isolate RP1 from oil-spilled garden soil is Gram-staining-positive with a distinct earthy odor, melanin formation, and white filamentous colonies. It has a molecular size of ~621 bp and 100% sequence similarity to many Streptomyces spp. Morphological, biochemical, and 16 S rRNA analysis confirmed it as Streptomyces sp. RP1, showing positive results in all screenings, including high emulsification activity against kerosene (27.2%) and engine oil (95.8%), oil displacement efficiency against crude oil (7.45 cm), and a significant reduction in surface tension (56.7 dynes/cm). Streptomyces sp. RP1 can utilize citrate as a carbon source, tolerate sodium chloride, resist lysozyme, degrade petroleum hydrocarbons, and produce biosurfactant at 37°C in a 15 mL medium culture, indicating great potential for bioremediation and various downstream industrial applications with optimization.
Mangrove located near urban area is exposed to various industrial discharge including heavy metals. Mangrove soil is capable of accumulating and storing these heavy metals. Heavy metals are toxic and non-biodegradable, so their accumulations affect water quality, while bioaccumulation and bio-assimilation of heavy metals in mangrove organisms negatively impact the food chain. Bacteria-derived biosurfactants are compounds capable of removing heavy metals from soil and sediment. Furthermore, environmentally friendly properties, such as biodegradability and low toxicity, exhibited by biosurfactants make them a suitable replacement for chemical surfactants for remediation efforts. This study was conducted to investigate the lead- (Pb) and zinc- (Zn) removing capability of rhamnolipid (RL), a type of biosurfactant produced by marine bacterium, Pseudomonas aeruginosa UMTKB-5. Rhamnolipid solutions of three different concentrations (25 mg/L, 50 mg/L and 75 mg/L) were added to mangrove soil and incubated for 7 days. The removal of Pb from soils was up to 18.3% using 25 mg/L RL solution, while 50 mg/L RL solution removed 48.3%, and 75 mg/L RL solution removed 75.9% Pb over time. Meanwhile, zinc removal of 25 mg/L RL solution was up to 24.9%, while 50 mg/L removed 16.5%, and 75 mg/L RL removed 30.5% of Zn. The results showed that RL from P. aeruginosa UMTKB-5 could be a potential biomaterial to be used to remediate heavy metals in sediment.
Phytoremediation is a biological remediation technique known for low-cost technology and environmentally friendly approach, which employs plants to extract, stabilise, and transform various compounds, such as potentially toxic elements (PTEs), in the soil or water. Recent developments in utilising chelating agents soil remediation have led to a renewed interest in chelate-induced phytoremediation. This review article summarises the roles of various chelating agents and the mechanisms of chelate-induced phytoremediation. This paper also discusses the recent findings on the impacts of chelating agents on PTEs uptake and plant growth and development in phytoremediation. It was found that the chelating agents have increased the rate of metal absorption and translocation up to 45% from roots to the aboveground plant parts during PTEs phytoremediation. Besides, it was also explored that the plants may experience some phytotoxicity after adding chelating agents to the soil. However, due to the leaching potential of synthetic chelating agents, the use of organic chelants have been explored to be used in PTEs phytoremediation. Finally, this paper also presents comprehensive insights on the significance of using chelating agents through SWOT analysis to discuss the advantages and limitations of chelate-induced phytoremediation.
Plant growth-promoting rhizobacteria (PGPR) mediate heavy metal tolerance and improve phytoextraction potential in plants. The present research was conducted to find the potential of bacterial strains in improving the growth and phytoextraction abilities of Brassica nigra (L.) K. Koch. in chromium contaminated soil. In this study, a total of 15 bacterial strains were isolated from heavy metal polluted soil and were screened for their heavy metal tolerance and plant growth promotion potential. The most efficient strain was identified by 16S rRNA gene sequencing and was identified as Bacillus cereus. The isolate also showed the potential to solubilize phosphate and synthesize siderophore, phytohormones (indole acetic acid, cytokinin, and abscisic acid), and osmolyte (proline and sugar) in chromium (Cr+3) supplemented medium. The results of the present study showed that chromium stress has negative effects on seed germination and plant growth in B. nigra while inoculation of B. cereus improved plant growth and reduced chromium toxicity. The increase in seed germination percentage, shoot length, and root length was 28.07%, 35.86%, 19.11% while the fresh and dry biomass of the plant increased by 48.00% and 62.16%, respectively, as compared to the uninoculated/control plants. The photosynthetic pigments were also improved by bacterial inoculation as compared to untreated stress-exposed plants, i.e., increase in chlorophyll a, chlorophyll b, chlorophyll a + b, and carotenoid was d 25.94%, 10.65%, 20.35%, and 44.30%, respectively. Bacterial inoculation also resulted in osmotic adjustment (proline 8.76% and sugar 28.71%) and maintained the membrane stability (51.39%) which was also indicated by reduced malondialdehyde content (59.53% decrease). The antioxidant enzyme activities were also improved to 35.90% (superoxide dismutase), 59.61% (peroxide), and 33.33% (catalase) in inoculated stress-exposed plants as compared to the control plants. B. cereus inoculation also improved the uptake, bioaccumulation, and translocation of Cr in the plant. Data showed that B. cereus also increased Cr content in the root (2.71-fold) and shoot (4.01-fold), its bioaccumulation (2.71-fold in root and 4.03-fold in the shoot) and translocation (40%) was also high in B. nigra. The data revealed that B. cereus is a multifarious PGPR that efficiently tolerates heavy metal ions (Cr+3) and it can be used to enhance the growth and phytoextraction potential of B. nigra in heavy metal contaminated soil.
Rhodovulum sulfidophilum was grown in settled undiluted and nonsterilized sardine processing wastewater (SPW). The aims were to evaluate the effects of inoculum size and media on the biomass production with simultaneous reduction of chemical oxygen demand (COD).